The term "flexible graphite" as used herein represents the exfoliated reaction product of rapidly heated graphite particles which have been treated with an agent that intercalates into the crystal structure of the graphite to expand the particles at least 80 or more time in the direction perpendicular to the carbon layers in the crystal structure. Flexible graphite may be compressed into thin sheets (hereinafter referred as "foil") with a density approaching theoretical density, although a density of about 70 lbs/ft.sup.3 is acceptable for most applications.
Flexible graphite possesses an appreciable degree of anisoptropy and heat insulating properties and is, accordingly, particularly useful for high temperature applications. However, upon rapid exposure to high temperature, flexible graphite foil may suffer an objectionable surface deformation phenomenon which takes the form of blistering. Blistering occurs on the surface of the flexible graphite foil when diffusion of thermally activated moisture adsorbed into the crystal structure is too slow to release the build up in desorbed gas pressure. This results in the delamination of the carbon layer planes at the surface of the foil causing the foil to blister. One method to minimize or eliminate blistering is to promote venting of the thermally adsorbed moisture by adjusting the physical parameters of the foil. This may be done by puncturing holes in the foil as taught and described in U.S. Pat. No. 4,752,518. Alternatively, one could change the density or thickness of the foil so that it is less dense and/or thinner than standard dimensions. These physical methods are objectionable in that they change the desired physical characteristics of the foil and will affect its heat insulating properties. The thermal environment to which the foil is subjected may also be controlled but this would minimize the utility of the foil.